Thermal release device such as an overload protection



A. R. MAIS 3,105,890

THERMAL RELEASE DEVICE SUCH AS AN OVERLOAD PROTECTION Oct. 1, 1963 Filed March 6, 1961 III United States Patent 3,105,390 THERMAL RELEASE DEVlCE SUCH AS AN OVERLOAD PRUTECTEUN Adolf Roli' lltiais, Enshedc, Sweden, assignor to Airfiebolaget Hagglund hz Sorter, Urnskoldsvik, Sweden, a corporation of Sweden Filed Mar. 6, 1961, Ser. No. 93,751 Claims priority, application wcden Mar. 14, 1960 6 (Ilaims. (Cl. zoo-12.2

The present invention relates to a thermal release device such as an overload protection in electrical installations, comprising a bi-metallic member for actuating a switch device, and a heater cartridge which is exchangeable and which is located in the vicinity of the b t-metallic member.

A release device of this kind is mainly designed to protect electric motors against overloading. The b-i-metallic member in this device is so dimensioned that it is heated in proportion to the extent that the motor which is to be protected is heated, namely by the motor current passing either through the bi-metallic member or through a separate heater member which transfers heat to the bimetallic member. The bending of the bi-rnetail caused by the heating is employed to actuate the switch member, which, when a certain maximum permissible current is exceeded, breaks the current supply to the [motor directly or by means of relays. Such a release device mustbe adjust able in accordance with the size of the motor. This, however, causes considerable difiiculty because the heat generated is proportional to the square of the current, and, if the heater member is as it should be, dimensioned to take the maximum current, the current can only be reduced insignificantly if sufiicient heat is to be generated to bend the bi-meta-l the required amount. In the most favourable case hitherto the ratio between the maximum and minimum value of the current has been 1:2. Usually, however, the ratio does not exceed 121.6, and a ratio of 1:1.3 or even less is by no means uncommon.

Attempts have already been made to increase, in the same release device, the ratio between the maximum and minimum value of the current by arranging an exchangeable heater cartridge in the vicinity of the bi-metallic member. However, in practice this proposal has not led to the desired result, partly because the heating effect on the bi-metallic member is dependent on external factors such as accumulation of dust on the members, i.e. dependent on a change in the heat transfer between the heater cartridge and the biametallic member during fairly lon operation, and partly because the bi-metallic member may be damaged either when the heater cartridge is exchanged or by direct damage because it is without mechanical protection. 2

The release device according to this invention solves this problem by virtue of the fact that the bi-metallic member is on all sides surrounded by a rigidly mounted body on which the heater cartridge is detachably threaded and held in place by a screw member. The release device according to the invention is distinguished by high accuracy and operational reliability even after a lengthy period. it can be adjusted to suit the size of the motor by merely disconnecting a screw-like part in the release device and exchanging the heater element, which can be done rapidly even by an unskilled person without the bimetallic member being damaged.

The invention is described in more detail in connection with the accompanying drawings, which show an embodiment. FIG. 1 is a section through the release device. FIG. 2 is a section of the device of FIG. 1 on the line l-I. FIG. 3 shows a part of the device according to FIGS. 1 and 2 seen from above.

Patented Oct. 1, 1963 The thermal overload device shown in the drawings is mounted on an insulation body 10 having a chamber 12 for receiving a heater cartridge 14, a chamber 16 through which a coupling strip 18 extends, and a chamber 2% in which switch members are located. The heater cartridge 14 consists of a ceramic tube 22 whose inner wall and both end surfaces are provided with a layer 24 of suitable resistor material. This resistor layer 24 may be a solid metal coating, perforated plate, a band wound around it or even turns of wire. Each end of the heater cartridge I14 is provided with a contact cap 26 which consists of good conducting metal and which is mounted on tube 22 by force fit so that suflicient contact pressure is obtained between the cap 26 and the resistor layer 24, which contact pressure is further increased when the heater cartridge is mounted in the release device. The cartridge is mounted in the chamber 12 on a socket 28 which is made of thermally conductive material and is closed at both ends with the exception of an upper aperture 32, which form a bearing for a wire spindle 34. The spindle 34 is at its upper end fixed to one end of a helically wound bi-metallic band 36, the other end of which is fixed to the lower part of the inner wall of socket 2 8 so that the twisting of the bi-metallic band when heated is transmitted to the spindle 34 The lower part of spindle 34 which projects out of the socket 28 is bent double to form a kind of crank 38 which extends into a. Windowlike aperture 4 0 in the coupling strip 18 and which, upon the spindle 34 being twisted, moves the strip to the right in FIG. 1. By means of this the switch mechanism in chamber 20, which is described later, is actuated.

The lower contact cap 26 of the heater cartridge 14 is in contact with an electricalconductor strip 42 while the upper contact cap 26 abuts a circular and screw-like disc 44 which has a threaded periphery and a diameter larger than the outer diameter of the contact caps 26. The latter disc 44 is screwed into another contact strip-46 and effects, when screwed home, the above mentioned further contact pressure between the two caps 26 and their associated contact strip 42 and contact disc 44 respectively. It can be clearly seen from FIG. 2 that the heater cartridge 14 can without difliculty be removed after unscrewing the disc 44, after which it can be exchanged for another heater cartridge.

The switch device in the chamber 20 consists of an angle arm 48 whose turning point is located on a slide member 50, which can be moved in height by means of an adjusting screw 52. One end of the angle arm 48 engages the coupling strip 18, while the other end forms a movable switch member 54, which cooperates with a fixed switch member 56. The movable switch member 54 is connected by a short conductor coil to a terminal member 58. By turning the adjusting screw 52 the angle arm 4-3 can be swung so as to adjust its position accurately in relation to the outer end of the coupling strip 18. The strip 18 is mounted in slot-like passages 60 in the body 10.

For the purpose of simplicity only one heater cartridge 14 with associated release device is shown in the drawin it is, however, possible to arrange several, for example three, beside each other, which are connected in a three-phase installation. The window-like apertures 40 in the coupling strip 18 permit each release device to operate the switch device in the chamber 20 separately by its crank 38 since the window 40 has such dimensions that any interaction between the crank members 38 is prevented.

It is of course possible for the heater cartridge 14 and disc 44 to be integral, that is the disc 44 is fixed to the upper cap 26, and this further facilitates exchange of the heater cartridge. A further modification consists in dorming the underside of the disc 44 with a collar into 3 which the heater cartridge is fitted before it is introduced into the hole in the conductor strip 46.

I claim:

1. A thermal relay comprising: a metallic housing having a cavity therein open at one end and closed at the other end, a bi-metal-lic element positioned entirely within the cavity on the axis thereof, a first conductor outside said housing adjacent the open end thereof, a second conductor outside said housing adjacent the closed end thereof, a threaded aperture in said second conductor coaxial with said housing, a heater cartridge in surrounding relation to said metallic housing, said cartridge comprising electric heating means having terminals at the ends of said heater cartridge, one of said terminals engaging said first conductor, an electrically conductive cap threaded into said aperture and engaging the other of said terminals, and an actuating member extending through the open end of said cavity and connected to said bi-metal1ic element.

2. A thermal relay comprising: a metallic housing having a cavity therein open at one end and closed at the other end, a bi-metallic element positioned entirely within the cavity on the axis thereof, a first conductor outside said housing adjacent the open end thereof, a second conductor outside said housing adjacent the closed end thereof, a threaded aperture in said second conductor coaxial with said housing, a heater cartridge in surrounding relation to said metallic housing, said cartridge comprising electric heating means having terminals at the ends of said heater cartridge, one of said terminals engaging said first conductor, an electrically conductive 'cap threaded into said aperture and engaging the other of said terminals, and spindle means rotatably mounted in said metallic housing and extending through the open end thereof and connected with said bimetallic element tfOl actuation thereby.

3. A thermal relay comprising: a metallic housing having a cavity therein open at one end and closed at the other end, a bi-meta1lic element positioned entirely within the cavity on the axis thereof, a first conductor outside said housing adjacent the open end thereof, a second conductor outside said housing adjacent the closed end thereof, a threaded aperture in said second conductor coaxial with said housing, a heater cartridge in surrounding relation to said metallic housing, said heater cartridge corn prising a ceramic tube, and resistance material on the inside of said ceramic tube and extending over the ends of said ceramic tube, conductive cap means mounted on the ends of said tube, one of said conductive cap means engaging said first conductor, an electrically conductive cap threaded into said aperture and engaging the other of said conductive cap means, and an actuating member extending through the open end of said cavity and connected to said bi-metaliic element.

4. A thermal relay comprising: a metallic housing having a cavity therein open at one end and closed at the other end, a bi-rnetallic element positioned entirely Within the cavity on the axis thereof, a first conductor outside said housing adjacent the open end thereof, a second conductor outside said housing adjacent the closed end thereof, a threaded aperture in said second conductor coaxial with said housing, a heater cartridge in surrounding relation to said metallic housing, said heater cartridge comprising a ceramic tube, resistance material on the inside of said ceramic tube and extending over the ends of said ceramic tube, conductive cap means mounted on the ends of said tube, one of said conductive cap means engaging said first conductor, an electrically conductive cap threaded into said aperture and engaging the other of said conductive cap means, an actuating member extending through the open end of said cavity and connected to said bimetailic element, and said conductive cap means engage by said conductive cap that is threaded into said second conductor being fixed to the said conductive cap whereby the entire heater cartridge is fixed to the said conductive cap.

5. A thermal relay comprising: a metallic housing having a cavity therein open at one end and closed at the other end, a bi-metallic element positioned entirely within the cavity on the axis thereof, a first conductor outside said housing adjacent the open end thereof, a second conductor outside said housing adjacent the closed end thereof, a threaded aperture in said second conductor coaxial With said housing, a tubular heater cartridge having an inside diameter larger than the outside diameter of said metallic housing and an outside diameter smaller than the diameter of said aperture in said second conductor whereby the cartridge can be introduced through the said aperture into surrounding relation to said metallic housing, said heater cartridge comprising a ceramic tube, resistance material extending the length of said tube on the inside and over the ends of said tube, metal caps on the ends of said tube forming terminals for the resistance material in the tube, one of said caps engaging said first conductor, and a conductive member threaded into said aperture and engaging the other of said caps and thereby effecting electrical connection of the said other cap with said second conductor.

6. A thermal relay comprising: a metallic housing having a cavity therein open at one end and closed at the other end, a binnetallic element positioned entirely within the cavity on the axis thereof, a first conductor outside said housing adjacent the open end thereof, a second conductor outside said housing adjacent the closed end thereof, a threaded aperture in said second conductor coaxial with said housing, a heater cartridge in surrounding relation to said metallic housing, said cartridge comprising electric heating means having terminals at the ends of said heater cartridge, one of said terminals engaging said first conductor, an electrically conductive cap threaded into said aperture and engaging the other of said terminals, spindle means rotatably mounted in said metallic housing and extending through the open end thereof and connected with said bi-metallic element for actuation thereby, a switch, and means connecting said switch vvith said spindle for actuation of the switch by the sp ndle in response to temperature changes induced in the bi-metailic element by the heater cartridge.

References Qited in the file of this patent UNITED STATES PATENTS 

1. A THERMAL REPLY COMPRISING: A METALLIC HOUSING HAVING A CAVITY THEREIN OPEN AT ONE END AND CLOSE AT THE OTHER END, A BI-METALLIC ELEMENT POSITIONED ENTIRELY WITHIN THE CAVITY ON THE AXIS THEREOF, A FIRST CONDUCTOR OUTSIDE SAID HOUSING ADJACENT THE OPEN END THEREOF, A SECOND CONDUCTOR OUTSIDE SAID HOUSING ADJACENT THE CLOSED END THEREOF, A THREADED APERTURE IN SAID SECOND CONDUCTOR COAXIAL WITH SAID HOUSING, A HEATER CARTRIDGE IN SURROUNDING RELATION TO SAID METALLIC HOUSING, SAID CARTRIDGE COMPRISING ELECTRIC HEATING MEANS HAVING TERMINALS AT THE ENDS OF SAID HEATER CARTRIDGE, ONE OF SAID TERMINALS ENGAGING SAID FIRST CONDUCTOR, AN ELECTRICALLY CONDUCTIVE CAP THREADED INTO SAID APERTURE AND ENGAGING THE OTHER OF SAID TERMINALS, AND AN ACTUATING MEMBER EXTENDING THROUGH THE OPEN END OF SAID CAVITY AND CONNECTED TO SAID BI-METALLIC ELEMENT. 